1. Field of the Invention
The present invention relates to an ink composition and an inkjet-recording method and a printed material using the same.
2. Description of the Related Art
Aqueous inkjet ink is lower in water resistance and often causes ink bleeding when printed on plain paper. It also had the problems that it was difficult to form an image when printed on a non-water absorbing recording medium such as plastic sheet because the ink droplet is adhered thereto weakly, it was necessary to dry the printed image without stacking of printed media immediately after printing because the solvent therein is vaporized extremely slowly, and thus, the image often causes ink bleeding.
Ultraviolet ray-hardening inks employing a multifunctional monomer superior in adhesiveness to recording medium were developed as the inks suitable for printing on non-water absorbing recording medium, but these inks, which were dispersed in water, were dried more slowly and could not give a favorable full color image. It has been practiced to use a volatile organic solvent as the ink solvent for improving the drying efficiency, but it was necessary to use a solvent, such as methylethylketone or ethanol, higher in volatility and flammability for further improvement in the drying efficiency.
Inkjet inks that harden and deposit not by vaporization of ink solvent but by irradiation of radiation ray were developed to solve these problems. For example, JP-A Nos. 2003-221528, 2003-221532, and 2003-221530 disclose inks containing a monomer having a polymerizable group and an oil-soluble dye. Alternatively, JP-A No. 2001-222105 discloses a photopolymerizable composition containing a photopolymerizable compound and a photopolymerization initiator. However, these inks still had a problem that the hardening speed was insufficient. Generally, radical polymerization, which is inhibited by oxygen, has a problem that the hardening efficiency of thin film was lower particularly in air.
For that reason, inks employing cationic polymerization, which is resistant to the inhibition by oxygen, were disclosed. For example, JP-A No. 2000-169552 discloses a high-energy ray-hardening composition containing oxirane and oxetane, but it is still insufficient in the hardening speed. Alternatively, JP-A No. 2001-220526 discloses a high-energy ray-hardening composition containing oxirane, oxetane, and a vinylether that was improved in hardening speed, but the composition had problems of deterioration of storage stability and generation of acetaldehyde by decomposition of the vinylether. On the other hand, JP-A No. 2004-10625 discloses a high-energy ray-hardening ink containing additionally a cyclic compound such as tetrahydrofuran, oxepane, or a monocyclic acetal, for improvement in storage stability, but it was still insufficient in hardening speed.